Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used in a wide variety of solvent applications such as drying, cleaning (e.g., the removal of flux residues from printed circuit boards), and vapor degreasing. Such materials have also been used in refrigeration and heat transfer processes. While these materials were initially believed to be environmentally benign, they have now been linked to ozone depletion. According to the Montreal Protocol and its attendant amendments, production and use of CFCs must be discontinued (see, e.g., P. S. Zurer, "Looming Ban on Production of CFCs, Halons Spurs Switch to Substitutes," Chemical & Engineering News, page 12, Nov. 15, 1993). The characteristics sought in replacements, in addition to low ozone depletion potential, typically have included boiling point ranges suitable for a variety of solvent cleaning applications, low flammability, and low toxicity. Solvent replacements also should have the ability to dissolve both hydrocarbon-based and fluorocarbon-based soils. Preferably, substitutes will also be low in toxicity, have no flash points (as measured by ASTM D3278-89), have acceptable stability for use in cleaning applications, and have short atmospheric lifetimes and low global warming potentials.
Certain perfluorinated (PFCs) and highly fluorinated hydrofluorocarbon (HFCs) materials have also been evaluated as CFC and HCFC replacements in solvent applications. While these compounds are generally sufficiently chemically stable, nontoxic and nonflammable to be used in solvent applications, PFCs tend to persist in the atmosphere, and PFCs and HFCs are generally less effective than CFCs and HCFCs for dissolving or dispersing hydrocarbon materials. Also, mixtures of PFCs or HFCs with hydrocarbons tend to be better solvents and dispersants for hydrocarbons than PFCs or HFCs alone.
Many azeotropes possess properties that make them useful solvents. For example, azeotropes have a constant boiling point, which avoids boiling temperature drift during processing and use. In addition, when a volume of an azeotrope is used as a solvent, the properties of the solvent remain constant because the composition of the solvent does not change. Azeotropes that are used as solvents also can be recovered conveniently by distillation.
There currently is a need for azeotrope or azeotrope-like compositions that can replace CFC- and HCFC-containing solvents. Preferably these compositions would be non-flammable, have good solvent power, cause no damage to the ozone layer and have a relatively short atmospheric lifetime so that they do not significantly contribute to global warming.